The present invention relates to an optical amplifying glass, an optical amplifying medium and a resin-coated optical amplifying medium. Particularly, it relates to an optical amplifying glass, an optical amplifying medium and a resin-coated optical amplifying medium, which are capable of amplification in a broad band for light with a wavelength of from 1.45 to 1.64 xcexcm.
For the purpose of application to an optical amplifier in an optical communication system, an optical amplifying medium (such as an optical amplifying fiber or an optical amplifying waveguide) comprising a clad glass and a core glass having a rare earth element doped, is being developed. Particularly, an optical amplifying medium wherein the above-mentioned rare earth element is Er (erbium), is actively being developed.
On the other hand, in order to cope with diversification of communication services expected in future, a wavelength division multiplexing optical communication system (WDM) has been proposed to increase the transmission capacity. In WDM, the transmission capacity increases as the number of wavelength division multiplexing channels increases. Accordingly, an optical amplifying medium is desired which is capable of amplification in a broad band for light with a wavelength of from 1.45 to 1.64 xcexcm.
In the case of a conventional Er-doped quartz type glass fiber, the wavelength width wherein an adequate gain is obtainable for light with a wavelength of from 1.45 to 1.64 xcexcm, is as narrow as from about 10 to 30 nm. Consequently, the number of wavelength division multiplexing channels is limited to a level of from 30 to 40 channels.
To obtain a larger wavelength width, an optical amplifier has been proposed wherein optical amplifying media having different gain spectra, are arranged in series to make amplification possible in a broad band. However, such an optical amplifier has had a problem such that the structure tends to be complex, or in the vicinity of the center of the wavelength range, there is a region where no amplification is possible.
Further, JP-A-8-110535 discloses an optical amplifying medium having a core glass made of an Er-doped tellurite type glass. For example, it is disclosed that with an optical amplifier glass fiber having a core glass having 1000 ppm of Er doped to a glass comprising TeO2 (75 mol %), ZnO (13 mol %), Na2O (3 mol %), Bi2O3 (4 mol %) and P2O5 (3 mol %), the gain became flat in a width of 70 nm from 1530 nm to 1600 nm (page 4, right column, lines 15-30).
However, the glass transition point of the tellurite type glass is likely to be low. For example, glass transition points of various tellurite type glasses are shown in Table 5 and Table 6 in Optical Materials 3 (1994) 193, whereby the maximum value is 343xc2x0 C., and the minimum value is 294xc2x0 C. If the glass transition point is low like this, the glass is likely to be thermally damaged when a laser beam having a high intensity is used as pumping light for optical amplification.
The present invention has an object to provide an optical amplifying glass and an optical amplifying medium, whereby a wavelength width wherein the gain is obtainable for light with a wavelength of from 1.45 to 1.64 xcexcm, is broad, and the above-mentioned thermal damage is unlikely to occur.
The present invention provides an optical amplifying glass comprising a matrix glass and, added thereto, from 0.01 wt % to 10 wt % of Er, characterized in that said matrix glass substantially comprises, as represented by mol %:
with the proviso that said matrix glass contains at least one of B2O3 and SiO2.
Further, the present invention provides an optical amplifying medium comprising a core glass and a clad glass, wherein a relation of:
0.0005xe2x89xa6(n1xe2x88x92n2)/n1xe2x89xa60.1
where n1 and n2 are refractive indices of the core glass and the clad glass, respectively, to light with a wavelength of 1.55 xcexcm, is satisfied, and the core glass is an optical amplifying glass comprising a matrix glass and, added thereto, from 0.01 wt % to 10 wt % of Er, characterized in that said matrix glass contains Bi2O3 within a range of from 20 mol % to 80 mol %, at least one of B2O3 and SiO2, and CeO2 within a range of from 0.01 mol % to 10 mol %.
Still further, the present invention provides a resin-coated optical amplifying medium characterized in that the above optical amplifying medium is covered with a resin.
With the optical amplifying glass of the present invention, typically, the wavelength width wherein the gain is obtainable for light with a wavelength of from 1.45 to 1.64 xcexcm (hereinafter, this wavelength width is referred to as xcex94xcex), is at least 80 nm. Further, its glass transition point is typically at least 360xc2x0 C.